1. Field of the Invention
The present invention relates generally to locking mechanisms and more particularly to an improved locking mechanism having means for detecting an attempted defeat of the lock by the insertion and turning of an unauthorized key or foreign object into the key slot and for generating a signal evidencing the violation.
2. Brief Description of the Prior Art
Inexpensive locking devices including pin tumbler, wafer-tumbler, disk-tumbler and Bramah type locks can be easily defeated by the manipulation of a properly constructed pick inserted into the looked keyway. Various means have thus heretofore been proposed to make it more difficult for such locks to be successfully opened by means other than a properly coded key. Furthermore, proposals have been made to distinguish between authorized and unauthorized objects inserted into the locked keyway for detecting a tamper attempt and providing a suitable response such as the activating of an alarm or the inhibiting of further lock movement.
One such approach is disclosed in the U.S. Patent to Frederick A. Sommer (U.S. Pat. No. 4,186,578) and includes the connection of an electrical circuit between two adjacent pin tumblers which are electrically insulated from the cylinder such that when the contacts are bridged by an electrical conductor such as a lock pick or the metal key, an electrical path is completed to produce the appropriate response to the tamper attempt. However, the problem with such apparatus is that it requires the use of a key made of plastic or other nonconductive material.
Another attempt to provide a means for detecting entry or drilling attempts into cylinder locks is disclosed in the U.S. Patent to Tobel (U.S. Pat. No. 4,262,506) and includes spring-biased tripping pins connected to an alarm or indicator system to detect a space in the rotated cylinder bore left unoccupied by insertion of an improperly made key or the removal of the cylinder. This approach has the disadvantage that it is only applicable to certain types of locks and does not provide a universal solution to the problem.